The present invention relates to laser beam receivers and, more particularly, to laser beam receiver units arranged to detect the presence and elevation of a rotating reference laser beam.
Rotating laser beams are commonly used in the fields of civil engineering, construction, agriculture, and surveying to establish a reference plane of light. U.S. Pat. No. 5,033,847, issued Jul. 23, 1991, illustrates a laser transmitter which provides such a rotating reference beam. Photosensitive laser beam receivers are frequently used to monitor the elevation of the reference plane of light. A conventional photosensitive laser beam receiver circuit is described in U.S. Pat. No. 4,693,598, issued Sep. 15, 1987. Many conventional laser receiver circuits employ a plurality of photodetectors disposed in a vertical row. The signals produced by the photodetectors in response to the incidence of a laser beam upon the detector array are utilized to provide an indication of the elevation of the laser beam. The indication may be displayed graphically in an array of LED's or as a numerical value on a visual display.
The above-described laser receivers are designed to provide an accurate indication of laser beam elevation. However, the accuracy of the elevation measurement is limited significantly if the laser receiver is not arranged in a vertical orientation. Indeed, it is often difficult for operators to position a laser receiver close to vertical because the associated terrain may skew their frame of reference. Further, it is often difficult for operators to maintain the receiver at vertical because adverse working conditions and physical constraints of the work environment may make it difficult to stabilize the receiver. Accordingly, there is a need for a laser receiver that is characterized by reduced vulnerability to environmental factors that lead to inadvertent, undetected, or undue laser receiver tilt.